Effects Of Dietary Calcium On The Blood Pressure Of Hypertensive Rats And Its Mechanisms

Many clinical investigations indicate that the deficient of dietary calcium could cause hypertension, and that the supplement of calcium might reduce blood pressure of hypertensive patients. Recent studies show that the decrease in GTPCH-1 expression levels and the abnormally increased GFRP level directly diminish the synthesis of BH₄ in aorta of hypertensive rats in lack of NO, dietary calcium may prevent and revert it.Our experiment is about the effects of dietary calcium on the BP, concentration of NO and activity of NOS in hypertensive rats in lack of NO. Through the observation of changes in BP, concentration of serum NO and activity of NOS, concentration of BH4 expression of mRNA of GTPCH-1 and GFRP, we investigated the possible mechanisms of the effects of dietary calcium on the BP.Methods Our experiment includes two steps: The experiment was accomplished in the Experimental Animal Laboratory and the Morphology Facility, Fourth Military Medical University of Chinese PLA. The first step, from October 22nd, 2005 to January 13th, 2006, twenty-four male SD rats were fed adaptively with basic forage and water in the temperature of 22℃for 2 weeks. Then they were randomized by weight into four groups equally(n=6):â‘ Control group: The rats were fed with basic forage and intragastric deionized water daily from the 1st week to the 6th week, and then stoped to lavage.â‘¡The rats were administrated with 5% dietary calcium and intragastric deionized water daily from the 1st week to the 6th week, and then stoped to lavage.â‘¢The rats were given with basic forage and 40 mg/kg L-NAME dissolving in the deionized water by intragastric administration from the 1st week to the 6th week, and then stoped to lavage, continued to be treated with 5% dietary calcium.â‘£From the 1st week to the 6th week, the rats were administrated with 40 mg/kg L-NAME dissolving in the deionized water intragastrically and basic forage, and then stoped to lavage, continued to be only treated with basic forage. All rats were fed at 8:30, lavaged at 19 o'clock and illuminated for 12h daily. BP was measured by RBP-1 type rat blood pressure apparatus every week. And 10 weeks later, all the rats were killed and the concentration of NO and activity of NOS were measured using by nitrate reductase.The second step, from March 30th to August 17th, 2006, after they were fed adaptively with basic forage and water in the temperature of 22℃for 2 weeks, 40 male SD rats at the age of 11 weeks were randomized by weight into five groups equally(n=8):â‘ The rats were given with 40 mg/kg L-NAME dissolving in the deionized water by intragastric administration and 5% dietary calcium from the 1st week to the 6th week, and then stoped to lavage.â‘¡The rats were administrated with basic forage and 40 mg/kg L-NAME dissolving in the deionized water by intragastric administration daily from the 1st week to the 6th week, and then stoped to lavage , continued to be only treated with 5% dietary calcium.â‘¢The rats were given with 40 mg/kg L-NAME dissolving in the deionized water by intragastric administration and basic forage from the 1st week to the 6th week, and then stoped to lavage.â‘£The rats were fed with basic forage and intragastric deionized water daily from the 1st week to the 6th week, and then stoped to lavage.⑤The rats were given with the deionized water by intragastric administration and 5% dietary calcium from the 1st week to the 6th week, and then stoped to lavage. All rats were fed at 8:30, lavaged at 19 o'clock and illuminated for 12h daily. BP was measured by RBP-1 type rat blood pressure apparatus every week. And 10 weeks later, all the rats were killed and the concentration of BH₄ and mRNA of GTPCH-land GFRP were detected by HPLC and RT-PCR respectively. The standard preparation of BH4 were bought from Sigma company in America, and the one-step kits of RT-PCR were bought from invitrogen company.Results Totally 24 rats were involved in the result analysis.â‘ BP: From the 4th week, BP was obviously higher in the second group and the third group than in control group and the first group (P<0.01); Between the 7th week and 10th week, the third group showed obviously higher BP than other three groups (P<0.01).â‘¡NO concentration: Compared with control group, the concentrations of NO were increased in the first group and the second group [(8.81±6.63), (14.80±5.32), (15.26±3.55)μmol/L, P<0.05], while declined in the third group [(2.89±1.71)μmol/L, P<0.05]; There was insignificant difference between the first group and the second group (P>0.05); The level of NO in the second group was higher than that of the third group (P<0.05).â‘¢NOS activity: Compared with contrpl group, the activities of NOS in the first group andhe second group were elevated [(334.57±74.35), (436.09±69.35), (448.76±45.68)μkat/L, P<0.05], but the level of NOS were declined in the third group [(255.88±35.17)μkat/L, P<0.05]. There was insignificant difference between the first group and the second group (P>0.05); The level of NOS in the second group was higher than that of the third group (P<0.05).â‘£BH₄ concentration: Compared with control group and the fourth group, the concentrations of BH₄ were decreased in the first group and the second group (P<0.01), the third group showed obviously lower BH₄ than other four groups (P<0.01).⑤GTPCH-â… concentration: Compared with control group and the fourth group, the concentrations of GTPCH-â… were decreased in the first group and the second group (P<0.05), the third group showed obviously lower GTPCH-â… than other four groups (P<0.05).â‘¥GFRP concentration: Compared with control group and the fourth group, the concentrations of GFRP were increased in the first group and the second group (P<0.05), the third group showed obviously higher GFRP than other four groups (P<0.05).Conclusionsâ‘ Dietary calcium can decrease the blood pressure of the hypertensive rats which lack of NO.â‘¡Dietary calcium can prevent the hypertension of rats induced by L-NAME.â‘¢Dietary calcium can decrease the blood pressure of the hypertensive rats which lack of NO by decreasing GFRP mRNA expression level, increasing GTPCH-1 mRNA expression levels, increasing the activities of BH4 and NOS and the synthesis of NO.